Comparative Genomic Analyses of 17 Clinical Isolates of Gardnerella vaginalis Provide Evidence of Multiple Genetically Isolated Clades Consistent with Subspeciation into Genovars

Author:

Ahmed Azad1,Earl Josh1,Retchless Adam1,Hillier Sharon L.23,Rabe Lorna K.2,Cherpes Thomas L.2,Powell Evan1,Janto Benjamin1,Eutsey Rory1,Hiller N. Luisa1,Boissy Robert1,Dahlgren Margaret E.1,Hall Barry G.14,Costerton J. William156,Post J. Christopher167,Hu Fen Z.167,Ehrlich Garth D.167

Affiliation:

1. Center for Genomic Sciences, Allegheny Singer Research Institute, Pittsburgh, Pennsylvania, USA

2. Magee-Womens Research Institute, Pittsburgh, Pennsylvania, USA

3. University of Pittsburgh, Pittsburgh, Pennsylvania, USA

4. Bellingham Institute, Bellingham, Washington, USA

5. Department of Orthopaedics, Allegheny General Hospital, Pittsburgh, Pennsylvania, USA

6. Departments of Microbiology and Immunology, Drexel University College of Medicine, Allegheny Campus, Pittsburgh, Pennsylvania, USA

7. Otolaryngology and Head and Neck Surgery, Drexel University College of Medicine, Allegheny Campus, Pittsburgh, Pennsylvania, USA

Abstract

ABSTRACT Gardnerella vaginalis is associated with a spectrum of clinical conditions, suggesting high degrees of genetic heterogeneity among stains. Seventeen G. vaginalis isolates were subjected to a battery of comparative genomic analyses to determine their level of relatedness. For each measure, the degree of difference among the G. vaginalis strains was the highest observed among 23 pathogenic bacterial species for which at least eight genomes are available. Genome sizes ranged from 1.491 to 1.716 Mb; GC contents ranged from 41.18% to 43.40%; and the core genome, consisting of only 746 genes, makes up only 51.6% of each strain's genome on average and accounts for only 27% of the species supragenome. Neighbor-grouping analyses, using both distributed gene possession data and core gene allelic data, each identified two major sets of strains, each of which is composed of two groups. Each of the four groups has its own characteristic genome size, GC ratio, and greatly expanded core gene content, making the genomic diversity of each group within the range for other bacterial species. To test whether these 4 groups corresponded to genetically isolated clades, we inferred the phylogeny of each distributed gene that was present in at least two strains and absent in at least two strains; this analysis identified frequent homologous recombination within groups but not between groups or sets. G. vaginalis appears to include four nonrecombining groups/clades of organisms with distinct gene pools and genomic properties, which may confer distinct ecological properties. Consequently, it may be appropriate to treat these four groups as separate species.

Publisher

American Society for Microbiology

Subject

Molecular Biology,Microbiology

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